In Win XP SP3 Control Panel I used the Date/Time control to reset the time correctly yesterday morning.
This morning I reboot and find that the clock in the status bar is, again, an hour slow.

In Win XP SP3 Control Panel I used the Date/Time control to check that:
(1) Time zone is GMT-5 (eastern USA & Canada)
(2) Automatically adjust clock for daylight saving changes is checked OFF
(3) Automatically synchronize with an Internet time server is checked OFF

Originally items (2) and (3) were checked ON.

I have a lurking feeling that this happened to me last year, or the year before.
I suspect that the lack of postings on this as an unresolved problem indicates that I have done something uniquely sinister to my system, but if anyone can suggest a different place to poke a stick at, I'd be happy to give it a try.

[quote name='chrisgreaves' post='765587' date='16-Mar-2009 08:46']I have a lurking feeling that this happened to me last year, or the year before.[/quote]
Some of those links have to do with file timestamp problems in Windows and I don't think that's what you're after, Chris. Windows, internet or not, knows to set or not set your clock to DST but the original will be still be going by the "pre-revision" of a couple of years ago.

If you haven't ever done so, you should consider downloading and installing the patch from MS for the revised DST dates. Otherwise, Windows will probably adjust you clock again when the "old" date rolls around.